Abstract
This work reports, for the first time, a dielectrophoresis (DEP) effect-induced motion of liquid crystal (LC) droplets in an LC/monomer mixture sample with a poly-(N-vinyl carbazole) PVK-coated substrate without an external voltage. With the UV pre-irradiation of the PVK layer through a binary mask, a laterally non-uniform electric field can be induced between the pre-illuminated regions and the neighboring non-pre-illuminated PVK regions near the borders of the two regions. The phase separation occurs once the temperature is lower than 50 °C and the LC droplets can form in the sample. The pre-formed non-uniform field provides a DEP-like force to manipulate the small LC microdroplets in the pre-illuminated regions to effectively migrate to the adjacent non-pre-illuminated regions. The continuous supply of the LC from the pre-illuminated regions to the adjacent non-pre-illuminated regions significantly increases the diffraction efficiency of the grating sample. This study provides an insight into developing new external-voltage-free DEP-based devices that can be applied on various fields, such as photonics, displays, and biomedicines.
Highlights
Dielectrophoresis (DEP) is a phenomenon in which a dielectric particle is subjected to a force in a non-uniform electric field [1,2,3,4,5]
Following cooling of the sample below 50 ◦ C, the liquid crystal (LC) droplets can form, and the non-uniform field may induce a DEP-like force. This force can drive the small LC microdroplets in the pre-illuminated regions to effectively move to the adjacent non-pre-illuminated regions, thereby significantly increasing the diffraction efficiency of the grating
The analysis shows that the non-uniform internal electric field plays a key role in effectively inducing the continuous output of the LC from the pre-illuminated regions and the continuous input of LC into the non-pre-illuminated regions
Summary
Dielectrophoresis (DEP) is a phenomenon in which a dielectric particle is subjected to a force in a non-uniform electric field [1,2,3,4,5]. In addition to displays and photonic devices, basic works on LCs have drawn increasing attention recently, the dynamically controllable movements of particles in LC media or LC droplets in dielectric media by use of DEP mechanisms [13,14,15]. Following cooling of the sample below 50 ◦ C, the LC droplets can form, and the non-uniform field may induce a DEP-like force. This force can drive the small LC microdroplets in the pre-illuminated regions to effectively move to the adjacent non-pre-illuminated regions, thereby significantly increasing the diffraction efficiency of the grating. The present DEP-like mechanism provides a new approach to controlling the movement of LC droplets with sizes ranging from micron to nanometer without the need of an external voltage
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